Notify NetworkStats only when interfaces changed in updateLinkProperties

In ConnectivityService, updateLinkProperties calls NetworkStats
even though the ip address or interface name has not changed and
only the tcp buffer size has changed. This is noisy and could
be problematic when RAT change occurs frequently, since when
RAT changes tcp buffer size configuration also changes.

This CL also fixes a wrong nullability annotation where the oldLp
of updateLinkProperties could be null when updateNetworkInfo
is called.

Test: atest ConnectivityServiceTest#testStatsIfacesChanged
Fix: 232048480
Change-Id: Ic226eb4a8aa1f38cba293510813f1cb55f0ea658

service/src/com/android/server/ConnectivityService.java

@@ -7435,7 +7435,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     }
 
     private void updateLinkProperties(NetworkAgentInfo networkAgent, @NonNull LinkProperties newLp,
-            @NonNull LinkProperties oldLp) {
+            @Nullable LinkProperties oldLp) {
         int netId = networkAgent.network.getNetId();
 
         // The NetworkAgent does not know whether clatd is running on its network or not, or whether
@@ -7487,7 +7487,13 @@ public class ConnectivityService extends IConnectivityManager.Stub
             }
             // Start or stop DNS64 detection and 464xlat according to network state.
             networkAgent.clatd.update();
-            notifyIfacesChangedForNetworkStats();
+            // Notify NSS when relevant events happened. Currently, NSS only cares about
+            // interface changed to update clat interfaces accounting.
+            final boolean interfacesChanged = oldLp == null
+                    || !Objects.equals(newLp.getAllInterfaceNames(), oldLp.getAllInterfaceNames());
+            if (interfacesChanged) {
+                notifyIfacesChangedForNetworkStats();
+            }
             networkAgent.networkMonitor().notifyLinkPropertiesChanged(
                     new LinkProperties(newLp, true /* parcelSensitiveFields */));
             notifyNetworkCallbacks(networkAgent, ConnectivityManager.CALLBACK_IP_CHANGED);
@@ -8246,7 +8252,8 @@ public class ConnectivityService extends IConnectivityManager.Stub
         }
     }
 
-    public void handleUpdateLinkProperties(NetworkAgentInfo nai, LinkProperties newLp) {
+    public void handleUpdateLinkProperties(@NonNull NetworkAgentInfo nai,
+            @NonNull LinkProperties newLp) {
         ensureRunningOnConnectivityServiceThread();
 
         if (!mNetworkAgentInfos.contains(nai)) {

service/src/com/android/server/connectivity/Nat464Xlat.java

@@ -22,6 +22,7 @@ import static android.net.NetworkCapabilities.TRANSPORT_TEST;
 import static com.android.net.module.util.CollectionUtils.contains;
 
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.net.ConnectivityManager;
 import android.net.IDnsResolver;
 import android.net.INetd;
@@ -420,7 +421,7 @@ public class Nat464Xlat {
      * This is necessary because the LinkProperties in mNetwork come from the transport layer, which
      * has no idea that 464xlat is running on top of it.
      */
-    public void fixupLinkProperties(@NonNull LinkProperties oldLp, @NonNull LinkProperties lp) {
+    public void fixupLinkProperties(@Nullable LinkProperties oldLp, @NonNull LinkProperties lp) {
         // This must be done even if clatd is not running, because otherwise shouldStartClat would
         // never return true.
         lp.setNat64Prefix(selectNat64Prefix());
@@ -433,6 +434,8 @@ public class Nat464Xlat {
         }
 
         Log.d(TAG, "clatd running, updating NAI for " + mIface);
+        // oldLp can't be null here since shouldStartClat checks null LinkProperties to start clat.
+        // Thus, the status won't pass isRunning check if the oldLp is null.
         for (LinkProperties stacked: oldLp.getStackedLinks()) {
             if (Objects.equals(mIface, stacked.getInterfaceName())) {
                 lp.addStackedLink(stacked);

tests/unit/java/com/android/server/ConnectivityServiceTest.java

@@ -7109,6 +7109,15 @@ public class ConnectivityServiceTest {
         expectNotifyNetworkStatus(onlyCell, MOBILE_IFNAME);
         reset(mStatsManager);
 
+        // Verify change fields other than interfaces does not trigger a notification to NSS.
+        cellLp.addLinkAddress(new LinkAddress("192.0.2.4/24"));
+        cellLp.addRoute(new RouteInfo((IpPrefix) null, InetAddress.getByName("192.0.2.4"),
+                MOBILE_IFNAME));
+        cellLp.setDnsServers(List.of(InetAddress.getAllByName("8.8.8.8")));
+        mCellNetworkAgent.sendLinkProperties(cellLp);
+        verifyNoMoreInteractions(mStatsManager);
+        reset(mStatsManager);
+
         // Default network switch should update ifaces.
         mWiFiNetworkAgent.connect(false);
         mWiFiNetworkAgent.sendLinkProperties(wifiLp);